1. Field of the Invention
This invention relates to joints for tubular members, and, more particularly, to joints for tubular members for the oil industry, such as tubing, casing and drill pipe, (hereinafter simply called "tubes" for convenience).
2. Description of the Prior Art
Commonly joints for these tubes are of spigot (or pin) and socket (or box) type, in which the socket is formed either from one end of each tube after enlargement (upsetting) and opening out, or from a short coupler, of larger diameter than the tubes, provided with a socket at each end. The connection is usually by screw threads of various configuration cut upon the spigot and within the socket, connection being made by "stabbing" the pin into the box and then rotating the pin relative to the box.
Sealing may be by means of a variety of metal to metal arrangements or by seal inserts or coatings. The tubes, and the joints, are usually formed of steel.
Such tubes often require to be connected into vertical strings of many thousands of feet which repeatedly have to be connected, and successively passed down a drill hole, and then subsequently removed therefrom and successively disconnected again during the exploration for and exploitation of oil or gas from the deep wells commonly encountered.
Such repeated connection and disconnection of the joints can cause considerable wear and tear to the joints, and the liability of damage to the threads by jamming and/or cross-threading, and damage to sealing surfaces of such joints.
Such damage can lead to reduced life of the tube before it requires re-preparation, on a shorter length, of the joint at each end, and a new coupler (if such is used), and can also lead to operational difficulties with respect to the connection and disconnection of the tubes themselves. Again such damage can, in the case of damage to the primary seal mechanism, result in oil or gas leakage through the joint which can be of serious environmental significance. Yet again any such damage resulting in a defect in the bore of the tube adjacent to the joint connection can lead to a corrosion weak spot with respect to the oil or gas product flowing therethrough, which can in due course significantly increase the damage to the joint.
It is an object of the present invention to provide a joint for oil and gas industry tubes which overcomes or at least substantially reduces the abovementioned disadvantages and difficulties.